OBJECTIVE: To study the biochemical mechanism of in vitro transformation in variants subcloned from BALB 3T3 for the purpose of understanding their variabilities in response to chemical carcinogens. APPROACH: (1) Study the metabolic activation of benzo(a)pyrene (BP) in variants by measuring their induced aryl hydrocarbon hydroxylase activities; (2) use high-pressure liquid chromatography (HPLC) to analyze metabolites; (3) variants were treated with BP, and their DNA was isolated to compare the amounts of carcinogen bound to DNA; (4) isolate and identify carcinogen-nucleoside adducts, (5) measure the excision repair in variants.